This invention relates to techniques for encoding on print media information relating to the physical characteristics (type) of media, and for automatically selecting a print mode of a printer based upon detection of that information.
Ink-jet printers are popular and cost-effective devices for producing black-and-white and color images. An ink-jet printer may include one or more ink-filled cartridges. The cartridges are mounted to a carriage in the printer body. Normally, the carriage is scanned across the width of the printer as paper or other print media is advanced through the printer. Each ink-filled cartridge includes at least one print head that is driven by signals from the printer""s processor to expel droplets of ink through an array of nozzles. The timing of the droplets are controlled to generate the desired text or image output on the print media.
In addition to traditional cut-paper stock, there are several other types of print media that are used with modern printers. For instance, one media type, known as a xe2x80x9ctransparency,xe2x80x9d is typically formed of a polyethylene terephtalate (PET) film and is used for overhead projectors and the like. Such media, as compared to typical paper stock, is glossy and has different ink absorbance. As a result, printing an image on a transparency type of media is best done using a print mode that includes multiple passes of the carriage so that part of the image is printed with each pass, thereby enhancing the drying of the ink on this media. This multiple pass approach is an example of a printer""s mode of operation (print mode), which is selected as a function of the type of print media that is presented to the printer.
The quality of color printing by ink-jet type printers has advanced to a level such that photo-quality images can be produced. To this end, special print media, hereafter collectively referred to as xe2x80x9cphoto media,xe2x80x9d has been developed for best emulating the glossiness, depth of color, etc of a conventional photograph. Printing a color image on photo media may call for different color mapping than might be used to print the same color image on another type of print medium. For example, a green element of the image may be printed with three yellow-ink droplets and two cyan-ink droplets on one media type. That same green element may require two yellow-ink droplets and three cyan-ink droplets if the same image were printed on photo media. Such color mapping, which is controlled by the printer""s processor, is another example of a print mode that is dependent upon the type of print media provided to the printer.
There are many different types of transparencies, although most of these types may be printed using the same print mode. The same is true for photo media printing. A good share of the different types of photo media may be printed with the same print mode. Certain types of media, however, have specific print mode requirements (a particularly unique color map, for instance) that may not be met with more common print modes that are used for printing groups of media types.
One way of ascertaining the type of print media that is provided to the printer (and thereafter selecting the appropriate print mode) is to encode the media with machine-readable information that is indicative of the media type. The information may be provided by coding that is applied to each sheet of the media with ink or other marking fluid that is invisible to the naked eye.
For instance, the margins of the sheet may be printed with a fluorescent bar code that is excited by ultraviolet radiation to emit visible light. Alternatively, an infrared fluorescent marking, which is excited by infrared radiation to emit such radiation, could be applied to the sheet as its identifying bar code. There are may other ways of invisibly encoding the media.
A printer may be equipped with a reader that is capable of detecting invisible code. The reader is positioned to detect the code of the print media that is about to enter the printer. The media-type information carried in the code is then used in selecting the print mode to be employed by the printer for such media.
In an automatic print mode selection system just outlined, which reads the media-type identification information encoded on the print media, it is desirable to ensure that existing printers can select a proper print mode for new media. Moreover, the print mode selection system should minimize the amount of information-storage space required for carrying out the print mode selection. In particular, the system should minimize the number of bits needed for media-type encoding, while providing error correction.
The present invention provides a technique for efficiently encoding the media-type information (hereafter referred to as identifier code) on print media, and for processing that information, once read, to select the appropriate print mode to be employed.
The system of the present invention minimizes storage space in the printer by using a small look-up table and a simple algorithm for selecting the correct print mode for any type of print media provided to the printer.
The system thus eliminates the relatively large storage space requirements that would otherwise be needed if all known media types were tabulated, and such tabulation were used in the printer as a large look-up table for matching media identifier code with a particular media type in the table. In a preferred embodiment, a two-dimensional matrix is constructed for storing known identifier codes with associated print modes. One dimension of the matrix (which can also be considered a column address of a table) is incremented in units that correspond to half of the identifier code of the media. Similarly, the other dimension of the matrix (row addresses of a table) is incremented in units that correspond to the other half of the identifier code of the media. Thus, in its simplest implementation the identifier code on a sheet of media is the concatenation of two matrix dimensions, which point to a single location in the matrix (or cell in the table).
Similar types of media are grouped together in the matrix. For instance, all known transparencies may be grouped in the upper left portion of the matrix and all known photo media are grouped in the lower right portion of the matrix. These clusters of media are thus related by ranges of identifier code.
A very small subset of the just-described matrix is stored in the printer memory. This subset contains only the identifier codes of particular print media that require print modes that are different from other media of the same type. This table may include, for example, three or four entries, as compared to the matrix, which may have over four-thousand entries.
In a preferred embodiment, the identifier code is comprised of twelve binary data bits. Each location in the matrix is addressed by two, six-bit units. Moreover, the encoding is established using cyclic binary code (Gray Code) thereby to enhance error rejection and eliminate the need for additional error correction bits.
The printer reads the media-type identifier code carried on a sheet. The small look-up table is then consulted. If a match is found, the printer controls the carriage and/or print heads in accordance with the associated print mode.
If a match in the look-up table is not found, the system of the present invention utilizes a simple algorithm for determining media-type information (and associated print mode) in a manner that facilitates a rapid determination of the print mode that is best suited for the media entering the printer. It will be appreciated that this aspect of the invention ensures that the system will carry with it the advantage of backward compatibility by assigning the correct print mode to print media that may developed in the future and at that time assigned its own unique, previously unknown identifier code.
Other advantages and features of the present invention will become clear upon study of the following portion of this specification and the drawings.